This Java applet demonstrates the harmonics of the air in a tube as an example of standing longitudinal waves. It illustrates the movement of the molecules in the air during such an oscillation. (Obviously the particles in reality move much shorter distances, and the real movement is very quick.) The nodes, i.e. the places where the particles don't move, are marked with "N". "A" means an antinode, i.e. a place where the particles oscillate with maximal amplitude. Note that at an open end of the tube there is always an antinode, at a closed end, however, a node!

You can select the form of the tube by using the appropriate radio buttons ("both sides open", "one side open"
and "both dides closed"). It is possible to switch to the next harmonic by pressing the button "Lower" respectively "Higher". The applet shows the harmonics up to the fifth upper oscillation.

If you write a new value for the length of the tube into the
textfield and press the "Enter" key, the applet will calculate wavelength and frequency. The speed of sound was presupposed as 343.5 m/s, corresponding to a temperature of 20 °C. The influence of the tube's diameter is neglected.